Metal vapor coating apparatus



June 20, 1967 K. c. TAYLOR $326,177

METAL VAPOR COATING APPARATUS Filed Sept. 12, 1963 INVENTOR. KEA/D/P/CK C. TAYLOR MWSM ATTORNEY United States Patent 3,326,177 METAL VAPOR CGATING APPARATUS Kendrick C. Taylor, Oreland, Pa., assignor, by mesne assignments, to Pennsalt Chemicals Corporation, Philadelphia, Pa, a corporation of Pennsylvania Filed Sept. 12, 18 63, Ser. No. 308,550 4 Claims. (Ci. 11849.1)

This invention relates to a new and improved method of and apparatus for coating metals and/or other conducting substrates and more particularly to the coating of both sides of a metal strip with different thicknesses for the coatings on each side.

In the past, metal such as iron has been galvanized by immersing the metal in a bath of zinc, covered with a flux, at a temperature of 425 to 500 C. This process had the limitation that equal thicknesses were deposited on both sides of the metal.

Further, the hot dipping process discussed above was only continuous for thicknesses above .001 inch. When the desired thickness was less than .001 inch, the coating became discontinuous. Further, it was necessary to allow for the action of the fluxes for control of the zinc iron interface and for thickness control so that the speed of the galvanizing line was limited to three to four hundred feet per minute. Further, it was not economically feasible to differentially coat the metal.

Differential coating of metal is desirable as a commercial solution to the automation of resistance welding. Thus, in resistance welding, the zinc which comes in contact with the copper electrodes of the resistance welder should be minimized. The zinc attacks these electrodes. Thus, only 8% of the copper electrode life is realized when a typical hot dipped galvanized coating of one ounce per square foot per side is resistance welded to another such sheet. Further, galvanizing by the hot dipping method gives a roughened surface so that it becomes difficult to paint thereover.

The galvanizing of iron with zinc by electrodeposition from cold sulfate solutions has the same faults as the hot dipping process mentioned above. In either the electrodeposition or the hot dipping processes, the only way differential coating is presently feasible is by masking one side and coating the other and then reversing the process. Such processes are at a cost premium compared to the present invention.

Therefore, it is the general object of this invention to provide a new and improved method of coating metal vapors to an electrically conducting substrate.

Still another object of this invention is the provision of a new and better coating apparatus capable of speeds up to two thousand feet per minute.

A further object of this invention is the provision of a new and better coating apparatus which will coat a metal substrate with a coating less than .001 inch.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

In the drawing, there is shown a cross sectional View of the coating apparatus of the present invention generally designated by the numeral 10.

The apparatus 10 includes a main coating housing 12 and an entrance and exit housing 14 integral therewith. It will be understood that the main housing 12 and the entrance and exit housing 14 may be vertically disposed and opposed to the horizontal disposition shown in the drawing. The entrance and exit housing 14 has a delivery opening 16 and an exit opening 18 on one Wall 20' thereof.

A sheet 22 of conducting material such as iron or steel which is to form the substrate of a finished product 24 coated on both sides thereof is supplied through the delivery opening 16 to the housing 14. The finished product 24 leaves the coating apparatus 10 of the present invention through the exit opening 18.

The sheet 22 and finished product 24 pass through a suitable first rotary seal 26 which isolates a first vacuum chamber 28 within the housing 14 from the atmosphere. A pump 30 evacuates the first vacuum chamber 28. A second rotary seal 32 through which the sheet 22 and finished product 24 pass separates the first vacuum chamber 28 from a second vacuum chamber 34 which still further reduces the pressure within the chamber 14.

The sheet 22 passes between a lowermost roll 36 and a center roll 38 of .a third rotary seal 40. The finished product 24 passes between the uppermost roll 42 of the rotary seal 40 and the center roll 38 thereof. It should be noted that the rotary seals 26, 32 and 40 are exactly similar in their sealing operation in that the rolls are all moving in the direction of the sheet 22 and the finished product 24 at the points of contact therewith.

The rotary seal between rollers 42 and 38 separates vacuum chamber 34 from a finished product vacuum chamber 44 through which passes the finished product 24. The rollers 38 and 36 separate second vacuum chamber 34 from a sheet cleaning chamber 46. The finished product vacuum chamber 44 and sheet cleaning chamber 46 are separated by a suitable barrier 48 and are closed at the end opposite from rotary seal 40 by a fourth rotary seal 50. The finished product 24 and sheet 22 pass through the rotary seal 50 in the same manner as was discussed With respect to third rotary seal 40.

The second vacuum chamber 34 is evacuated by a sec ond pump 52.

A suitable reducing gas such as hydrogen is supplied to the sheet cleaning chamber 46 through a conduit 56 spaced adjacent the fourth rotary seal 50. The finished product vacuum chamber 44 and sheet cleaning chamber 46 have a common opening 58 connected to a vacuum pump 54 for evacuating the chamber 44 and maintaining the pressure within the sheet cleaning chamber 46 at a low value. The opening 58 is near the third seal 40 so that the flow of the reducing gas entering through conduit 56 is away from the fourth seal 50 thusaiding in maintaining low vacuum in the main housing 12.

A plurality of plates 60 are provided on opposite sides of the sheet 22 and equally spaced therefrom for cleaning the sheet 22 in a manner to be discussed below. 7

The plates 60 are connected to the positive terminal of a battery 62 whose negative terminal is connected to the grounded lowermost roll 36 of third rotary seal 40. Roll 36 is in continuous electrical contact with the sheet 22. Thus, sheet 22 acts as a cathode as it passes between the plates 60. Battery 62 may range in voltage between and 3000 volts in accordance with the spacing of the plates 60.

The sheet 22 of metal may have a layer of metal oxide and/or organic contaminates thereon. It is essential for good coating of the sheet that these layers be cleaned from the sheet on both sides thereof. The plates 60 with the voltage placed thereon by battery '62 creates a glow discharge between the plates 60 and the sheet 22 on opposite sides thereof. The sheet 22 will act as a cathode and there will be electron flow from the cathodic sheet 22 to the plates 60. In the reducing atmosphere of hydrogen within the sheet cleaning chamber 46, the oxide coating is thereby removed. The water vapor produced by the reaction of the hydrogen with the oxides will be removed through the opening 58 by third vacuum pump 54.

Further, the ions which will fiow from the anodes or plates 60 to the cathodic sheet 22 will physically bombard the sheet 22 in a manner which will loosen and thus remove any organic contaminates on the sheet 22. In this manner, the oxide coating and the organic contaminates on sheet 22 are removed from both sides thereof in a simple and easy manner. Since the roll 36 is grounded, there is no danger of shock to persons coming in contact with components of the apparatus 10. The cleaned sheet 22 then passes into main housing 12 which is evacuated by a suitable fourth vacuum pump 64.

The sheet 22 passes over two spaced conducting rolls 66 and 68 which are electrically connected to a battery 70. The battery 70 will act to supply high current through the sheet 22 which will resistance heat the sheet to a predetermined temperature. This step of preheating the sheet to a temperature such as between 350 and 600 F. is necessary if the sheet 22 is to be coated with a metal whose thickness is one mill or greater. Other factors affecting preheating are degree of cleanliness of sheet 22 and surface adhesion coeflicient or other characteristic of the coating material.

The now preheated sheet 22 passes over a feed roller 72. One exposed side 74 of the sheet 22 then passes over a coating metal vaporizing boat 76.

While the conducting substrate sheet 22 of the present invention is preferably strip steel, it will be understood that other metals may be utilized therefor. Further, the present invention in its preferred form utilizes Zinc as the material within the boat 76. However, chromium, nickel, tin, or other metals might also be utilized by the process of the present invention. The strip 22 passes over the boat 76 in a horizontal plane so as to insure constant spacing of the side 74 from the boat 76. In a preferred embodiment of the present invention, the boat 76 was spaced ten inches from the downwardly facing side 74.

The boat 76 is heated to the temperature at which the zinc evaporates at the pressure within the main chamber 12. The zinc will be heated above the vaporization temperature for the pressure of the chamber 12. For example, zinc vaporizes at a temperature of 343 C. to 405 C. over a pressure range of .01 millimeter of mercury to .1 millimeter of mercury respectively. At such pressure, the zinc would be superheated to temperatures in excess of 405 C. It will be understood that the side 74 of the sheet 22 must be at a temperature less than the vaporization temperature of the zinc coating material in order to achieve vapor deposition thereon. The amount of material deposited on the side 74 can be varied by varying the temperature in the boat 76, the size of the surface of the zinc in the boat 76 exposed to the side 74, or by the provision of a mask spaced from the boat 76 to limit the exposed surface of the side 74. However, the step of controlling the amount of coating material which is deposited on the side 74 of the sheet 22 as it passes over the boat 76 is considered a part of the present invention. The sheet 22 with its coating 78 on one side 72 thereof then passes over a roller 80 so that the other side 82 of the sheet 22 is then horizontally disposed over a second coating metal vaporizing boat 84 which will deposit a coating 86 on the side 82. The boat 84 is similar to the boat 76 but may be differently controlled from the boat 76 so as to achieve a different coating 86 on the side 82 than the coating 78 achieved on the side 72 of the sheet 22. Thus, the sheet 22 after it leaves the boat 84 will have become the finished product 24 which has two coatings 78 and 86 on opposite sides thereof which coatings may be different in thickness and/ or material. The now coated sheet 22 (finished product 24) passes around rollers 88 and 90 and through rotary seal 50 into the finished product vacuum chamber 44. The finished product 24 continues out of the apparatus through third rotary seal 40, second vacuum chamber 34, second rotary seal 32, first vacuum chamber 28, first rotary seal 26 and exit opening 18.

Thus, the objects of the present invention have been achieved by the provision of a method for an apparatus of coating a metal substrate with a metal vapor wherein the coating may have different thicknesses on opposite sides thereof, and the coating can be less than 1 mil (.001 inch). Further, this can be achieved at a speed of two thousand feet per minute. The metal substrate is cleaned prior to the coating, and may be preheated if necessray.

It is within the scope of the present invention to have the housing 12 upright as opposed to the horizontal disposition illustrated. In that case, the portions of sheet 22 and product 24 between rollers 68, 72, 80, 88 and 90 would be vertically disposed. In such an arrangement, it is easier to control the tension in sheet 22 and deflector plates will be provided above boats 76 and 84.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the fore going specification as indicating the scope of the invention.

I claim:

1. Coating apparatus comprising first and second vacuum chambers, a controlled vapor deposition means in said first chamber for vapor depositing a coating on at least one side of the stripe, said second vacuum chamber having first seal means for passing a strip into said second vacuum chamber and a second seal means for passing the strip in said second vacuum chamber into said first vacuum chamber, cleaning means in said second vacuum chamber for cleaning at least one side of said strip prior to passage of the strip through said second seal means, said cleaning means including electrically conducting plates spaced from opposite sides of said strip as said strip passes through said second vacuum chamber, and means for applying an electric potential to said electrically conducting plates to thereby provide a glow discharge between opposite sides of said strip and said electrically conducting plates, said cleaning means further including means for supplying a reducing gas into said second vacuum chamber and means for removing said reducing gas from said vacuum chamber to maintain low pressure in said vacuum chamber, said first seal means including a rotary seal, means for connecting said rotary seal to said electric potential means, said rotary seal being in electrically conducting relation with the strip as it passes into said second vacuum chamber, said means for supplying a reducing gas to said second vacuum chamber being mounted adjacent said second seal means, and said means for evacuating said second vacuum chamber being mounted adjacent said rotary seal.

2. Coating apparatus in accordance with claim 1 wherein said first and second seal means each comprises three vertically disposed rollers, said strip passing between a first roller and a central roller of each seal when passing into said second vacuum chamber and said first vacuum chamber, and between a second roller and the central roller of each seal when passing out of said first vacuum chamber and said second vacuum chamber.

3. Coating apparatus comprising first and second vacuum chambers, a controlled vapor deposition means in said first chamber for vapor depositing a coating on at least one side of a strip, said second vacuum chamber having first seal means for passing a strip into said second vacuum chamber and a second seal means for passing the strip in said second vacuum chamber into said first vacuum chamber, cleaning means in said second vacuum chamber for cleaning at least one side of said strip prior to passage of the strip through said second seal means, said cleaning means including electrically conducting plates spaced from opposite sides of said strip as said strip passes through said second vacuum chamber, and means for applying an electric potential to said electrically conducting plates to thereby provide a glow discharge between opposite sides of said strip and said electrically conducting plates, said cleaning means further including means for supplying a reducing gas into said second vacuum chamber and means for removing said reducing gas from said vacuum chamber to maintain low pressure in said vacuum chamber, said first seal means including a rotary seal, means for connecting said rotary seal to an electric potential means, said rotary seal being in electrically conducting relation with the strip as it passes into said second vacuum chamber.

4. Coating apparatus in accordance with claim 3 wherein said first and second seal means each comprises three vertically disposed rollers, said strip passing between a first roller and a central roller of each seal when passing into said second vacuum chamber and said first vacuum chamber, and between a second roller and the central roller of each seal when passing out of said first vacuum chamber and said second vacuum chamber.

References Cited UNITED STATES PATENTS Stoll 117-107.1 McMannus et a1. 117107.1 X Toulmin 117107.1 X Scott 117107.1 X Vodonik 11793.1 X Hnilicka 117107.l Jenkins 11750 Smith et al 117107 X Brick l17107.1 X Brick et al 11710'7.1 X

ALFRED L. LEAVITT, Primary Examiner.

RALPH S. KENDALL, Examiner. 

1. COATING APPARATUS COMPRISING FIRST AND SECOND VACUUM CHAMBERS, A CONTROLLED VAPRO DEPOSITION MEANS IN SAID FIRST CHAMBER FOR VAPOR DEPOSITING A COATING ON AT LEAST ONE SIDE OF THE STRIPE, SAID SECOND VACUUM CHAMBER HAVING FIRST SEAL MEANS FOR PASSING A STRIP INTO SAID SECOND VACUUM CHAMBER AND A SECOND SEAL MEANS FOR PASSING THE STRIP IN SAID SECOND VACUUM CHAMBER INTO SAID FIRST VACUUM CHAMBER, CLEANING MEANS IN SAID SECOND VACUUM CHAMBER FOR CLEANING AT LEAST ONE SIDE OF SAID STRIP PRIOR TO PASSAGE OF THE STRIP THROUGH SAID SECOND SEAL MEANS, SAID CLEANING MEANS INCLUDING ELECTRICALLY CONDUCTING PLATES SPACED FROM OPPOSITE SIDES OF SAID STRIP AS SAID STRIP PASSES THROUGH SAID SECOND VACUUM CHAMBER, AND MEANS FOR APPLYING AN ELECTRIC POTENTIAL TO SAID ELECTRICALLY CONDUCTING PLATES TO THEREBY PROVIDE A BLOW DISCHARGE BETWEEN OPPOSITE SIDES OF SAID STRIP AND SAID ELECTRICALLY CONDUCTING PLATES, SAID CLEANING MEANS FURTHER INCLUDING MEANS FOR SUPPLYING A REDUCING GS INTO SAID SECOND VACUUM CHAMBER AND MEANS FOR REMOVING SAID REDUCING GAS FROM SAID VACUUM CHAMBER TO MAINTAIN LOW PRESSURE IN SAID VACUUM CHAMBER, SAID FIRST SEAL MEANS INCLUDING A ROTARY SEAL MEANS FOR CONNECTING SAID ROTARY SEAL TO SAID ELECTRIC POTENTIAL MEANS, SAID ROTARY SEAL BEING IN ELECTRICALLY CONDUCTING RELATION WITH THE STRIP AS IT PASSES INTO SAID SECOND VACUUM CHAMBER, SAID MEANS FOR SUPPLYING A REDUCING GAS TO SAID SECOND VACUUM CHAMBER BEING MOUNTED ADJACENT SAID SECOND SEAL MEANS, AND SAID MEANS FOR EVACUATING SAID SECOND VACUUM CHAMBER BEING MOUNTED ADJACENT SAID ROTARY SEAL. 